Sheet articles such as papers, credit cards, photographs and the like are usually processed by processing mechanisms, for example paper shredding mechanisms, scanning mechanisms or film laminating mechanisms. In a case that the sheet articles are too thick or too thin, the processing mechanisms may fail to normally function. For example, if thickness of the sheet article exceeds the allowable specification of the processing mechanism, the sheet article is readily jammed or the processing operation is possibly interrupted. The obstacle is eliminated with difficulty by the users themselves. Otherwise, the processing mechanism needs to be returned to the depot service, which increases inconvenience.
For solving these problems, some approaches have been proposed. Take a conventional paper shredding mechanism for example. Referring to FIG. 1, a schematic partial view of a paper shredding mechanism having a device for automatically detecting thickness of the sheet article according to the prior art is illustrated. As shown in FIG. 1, the paper shredding mechanism 10 principally includes two guide plates 121, 122, an operating element 13, an optical grating wheel 14 and an optical sensing module 15. A paper feeding channel 120 is defined between the guide plates 121 and 122. After an article sheet 11 such as a paper is fed into the paper feeding channel 120 through the entrance 1201, the front edge 111 of the paper 11 is sustained against a protrusion 131 of the movable operating element 13. Next, the protrusion 131 of the movable operating element 13 is pressed down by the front edge 111 of the paper 11, and thus the optical grating wheel 14 is driven by the rear end of the operating element 13 to render a rotation M in either a forward or backward direction. The protrusion 131 is continuously sustained against the paper 11 until the rear edge 112 of the paper 11 is separated from the protrusion 131. Meanwhile, the operating element 13 is returned to its original position. By detecting rotation M of the optical grating wheel 14 and the rotational displacement thereof, the optical sensing module 15 may discriminate the thickness of the paper 11. In a case that the thickness lies within the acceptable range of the paper shredding mechanism 10, the paper shredding mechanism 10 maintains its normal operations. Whereas, in another case that the thickness of the sheet article exceeds the allowable specification of the processing mechanism, the follow-up processing operation (e.g. a paper shredding operation) will be interrupted.
The operation principles of the optical grating wheel 14, the optical sensing module 15 and the shredding operations are known in the art, and not redundantly described herein.
The paper shredding mechanism 10, however, still has some drawbacks. For example, when the front edge 111 of the paper 11 leaves the exit 1202 of the paper feeding channel 120, a shredding knife member, which is composed of for example two knifes arranged in a staggered form, starts a shredding operation. Under this circumstance, the rear edge 112 of the paper 11 is readily subject to a flapping effect. That is, the paper 11 is swung to the left and right sides in the direction F1.
Due to the flapping effect, the protrusion 131 is unstable if the rear edge 112 of the paper 11 has not been fully separated from the protrusion 131. As a consequence, the thickness of the paper 11 is often erroneously discriminated. In other words, even if the thickness lies within the acceptable range of the paper shredding mechanism 10, the thickness of the paper 11 may be erroneously discriminated due to the flapping effect of the rear edge 112 of the paper 11. Under this circumstance, the shredding operation of the paper shredding mechanism 10 is likely to be erroneously interrupted.
For reducing the influence of the flapping effect, another paper shredding mechanism having a device for automatically detecting thickness of the sheet article is shown in FIG. 2. As shown in FIG. 2, the paper shredding mechanism 20 includes two guide plates 221, 222 and an operating element 23. A paper feeding channel 220 is defined between the guide plates 221 and 222. The thickness detecting device of FIG. 2 is distinguished from FIG. 1 by having two optical sensing modules 251 and 252. For clarification, only pins of these optical sensing modules 251 and 252 are shown in the drawings. The optical sensing modules 251 and 252 are fixed on a stationary plate 24. In addition, the light beams emitted from the optical sensing modules 251 and 252 may be sheltered by the operating element 23. During the paper 21 is transported across the paper feeding channel 220 from the entrance 2201 to the exit 2202, the paper 21 is sustained against the protrusion 231 of the operating element 23 such that the light beams from the optical sensing modules 251 and 252 are successively sheltered by the protrusion 231. Until these two optical sensing modules 251 and 252 are successively sheltered by the protrusion 231, the thickness of the paper 21 is deemed to exceed the acceptable range.
The operation principles of using the operating element 23 to shield these two optical sensing modules 251 and 252 are known in the art, and are not redundantly described herein.
There are some additional differences between the thickness detecting devices of FIG. 2 and FIG. 1. Please refer to FIG. 2 again. The paper shredding mechanism 20 further includes a cam 27, which is driven by a motor set 26. When the front edge 211 of the paper 21 leaves the exit 2202 of the paper feeding channel 220 and the shredding operation is started, the cam 27 is driven by the motor set 26 such that the protruding bar 271 of the cam 27 moves in the advancing direction F. Consequently, the push rod 28, which is sheathed by a spring 29, is pushed forward by the protruding bar 271 of the cam 27. The push rod 28 is continuously pushed forward by the protruding bar 271 of the cam 27 during the shredding operation of the front edge 211 of the paper 21 is performed. Even if the flapping effect is generated at this moment, the possibility of causing erroneous operation of the paper shredding mechanism 10 is reduced because the rear edge 212 of the paper 21 is no longer improperly sustained against the protrusion 231 of the operating element 23.
The paper shredding mechanism 20, however, still has some drawbacks. For example, the spring 29 is often suffered from elastic fatigue after used for a long term. That is, the reliability of the paper shredding mechanism 20 is gradually reduced as time has elapsed, and thus the paper 21 is likely to be improperly sustained against the operating element 23. Moreover, the paper shredding mechanism 20 of FIG. 2 is disadvantageous because it is not cost-effective and its structure is complicated. These disadvantages become hindrance from fabricating and commercializing the paper shredding mechanism 20.